The present invention relates to a method for controlling the molecular weight distribution of polyether glycol obtained in producing polyether glycol by ring-opening polymerization of tetrahydrofuran (hereinafter referred to as THF) as a starting monomer, using a heteropoly-acid as a catalyst.
Polyether glycol is an industrially useful polymer as the main raw material of polyurethanes used for polyurethane elastic fiber and synthetic leather, an additive for oil and a softening agent. Polyether glycol is required, in its industrial usage, to have an optimum molecular weight and optimum molecular weight distribution according to the intended uses.
U.S. Pat. Nos. 4,568,775, 4,568,065 and 5,416,240 disclose that heteropoly-acids can be used as a polymerization catalyst in producing polyether glycol. These prior art references disclose the activity of heteropoly-acids as a catalyst. JP-A-5-70585 discloses a method of controlling the average molecular weight of polyoxyalkylene glycol and the derivatives thereof by using a heteropoly-acid as a catalyst. However, none of these prior art references disclose a method for controlling the molecular weight distribution of the polyether glycol obtained.
One of the known methods for obtaining polyether glycol having an optimum narrow molecular weight distribution which can meet the various intended uses is, as disclosed in U.S. Pat. No. 5,053,553, a method wherein polytetramethylene-ether glycol (hereinafter referred to as PTMG) obtained by polymerization is subjected to liquid-liquid extraction using methanol, water and a specific nonpolar solvent to separate a solvent phase of the upper layer containing PTMG having a narrow molecular weight distribution, thereby to obtain PTMG having a narrow molecular weight distribution. In this method, however, in addition to the step of polymerization of polyether glycol, an extraction step and further a recovery step must be conducted; moreover, since an organic solvent is used, the cost for its recovery etc. must be added, leading to economical disadvantage.
Though polyether glycol is sometimes used independently as an additive and the like, it is mostly used as a reaction starting material. Therefore, a specified number average molecular weight and a specified molecular weight distribution are required according to intended uses.
In particular, when polyether glycol is used as the raw material for elastic fiber typically represented by polyurethane fiber, since the molecular weight distribution of polyether glycol exerts an influence on the elastic function, particularly on the recovery, of elastic fiber, a process for producing polyether glycol is awaited which can control the molecular weight distribution as desired.
The process for producing polyether glycol using a heteropoly-acid as a catalyst is attracting much attention, because it allows the presence of water in the reaction system and makes it possible to conduct polymerization in one stage reaction. In particular, in the production of polyether glycol using this catalyst, a process is eagerly desired which can precisely control the molecular weight distribution of the polymer.
The object of the present invention is to provide, in producing polyether glycol by using a heteropoly-acid as a catalyst, a method which can efficiently adjust the molecular weight distribution of the polyether glycol obtained to a specified value or into a specified range.
The present invention provides a method for controlling the molecular weight distribution of polyether glycol obtained which comprises, in a THF polymerization reaction system using a heteropoly-acid as a catalyst, making an amount of water which can form two phases, namely an organic phase (THF phase) and a catalyst phase, present in the reaction system, and controlling the residence time distribution of the starting monomer in the catalyst phase in the reaction vessel, thereby to control the molecular weight distribution of the polyether glycol obtained. namely a organic phase (THF place) and a catalyst phase, present in the reaction system, and controlling the residence time distribution of the starting monomer in the catalyst phase in the reaction vessel, thereby to control the molecular weight distribution of the polyether glycol obtained.
It is disclosed in JP-A-59-221326 that the amount of water coordinated to a heteropoly-acid influences the catalytic activity, and the amount of water coordinated to a heteropoly-acid and the number average molecular weight obtained by polymerizing THF are correlated to each other. However, though the above document describes that the molecular weight distribution of the polyether diol obtained is sharp, it describes nothing about the control of molecular weight distribution.
The present inventors have made extensive study on controlling the molecular weight distribution of polyether glycol obtained by polymerizing THF with maintaining the number of coordinated water of catalyst in the reaction system constant. As a result, it has been found out that the molecular weight distribution of polyether glycol can be precisely controlled without substantially changing its number average molecular weight by keeping the feed amount of the starting monomer THF relative to the catalyst phase approximately constant in the reaction vessel and controlling the residence time distribution of the starting monomer which reacts in the catalyst phase. The present invention has been accomplished on the basis of the above finding.
According to the present invention, there is provided a method for controlling the molecular weight distribution of polyether glycol obtained in producing polyether glycol having a specified number average molecular weight by polymerizing THF as a starting monomer with the use of a heteropoly-acid as a catalyst, which method comprises conducting the polymerization in the presence of an amount of water which can form two phases of the organic phase and the catalyst phase, sampling the polymerization product during the polymerization to determine the molecular weight distribution and, when the molecular weight distribution thus found is narrower than the specified molecular weight distribution, making the residence time distribution of the starting monomer in the catalyst phase wider, while, when the found molecular weight distribution is wider than the specified molecular weight distribution, making the residence time distribution of the starting monomer in the catalyst phase narrower.
According to the present invention, there is further provided a process for producing polyether glycol having a specified number average molecular weight and a specified molecular weight distribution by polymerizing tetrahydrofuran as a starting monomer with the use of a heteropoly-acid as a catalyst, which process comprises conducting the polymerization in the presence of an amount of water which can form two phases of the organic phase and the catalyst phase, sampling the polymerization product during the polymerization to determine the molecular weight distribution and, when the molecular weight distribution thus found is narrower than the specified molecular weight distribution, making the residence time distribution of the starting monomer in the catalyst phase wider, while, when the found molecular weight distribution is wider than the specified molecular weight distribution, making the residence time distribution of the starting monomer in the catalyst phase narrower.